1. Field of the Invention
The present invention relates to an aberration measuring apparatus for measuring aberration of a group lens set including an objective lens for use with an optical disk reproducing apparatus. The present invention also relates to an adjusting device for adjusting a position of a lens in a group lens set by using the aberration measuring apparatus when the group lens set consists of a plurality of lenses.
2. Description of the Related Art
A moving image with high definition and high quality sound can be recorded to an optical disk and reproduced from the optical disk, since digital technology has been developed in recent years. In accordance with this development, increase in memory capacity recorded to one optical disk is required. Accordingly, it is considered that recording and reproducing operations of high density are performed, by increasing a numerical aperture of an objective lens and reducing a spot diameter during the recording and reproducing operations. Therefore, a construction using a group lens set constructed by two lenses is required to increase the numerical aperture of the objective lens.
The group lens set has a large numerical aperture such as 0.75. This requires a high level of position adjustment in comparison with a spherical lens having a numerical aperture of about 0.5. Therefore, when the group lens set is assembled, it is necessary to manufacture the group lens set so that a position relation of the two lenses is adjusted by correctly evaluating an aberration. Such aberration are caused by a shift in an optical axis of the two lenses and distance between lenses of the lens set.
One example of a lens adjusting method is disclosed in Japanese Patent Laid-Open No. 10-255304. In this method, light is transmitted through the lenses, and the position relation of the lens is adjusted by moving one lens with respect to the other lens on the basis of the position and shape of a light spot picked up in an image pickup element, or on the basis of a diffraction pattern of the light.
However, in the adjusting method utilizing a converging spot, a problem exists in that it is difficult to determine a spot shape since the spot shape is small. Therefore, it is difficult to stably adjust the position relation on the basis of a diffraction pattern of the light.
Therefore, an adjusting method utilizing interference is also proposed instead of an observation of the spot shape. In this method, parallel light incident to the objective lens is once converged and is incident to a reference spherical surface, and is reflected on the reference spherical surface. The reflected light is then converted to parallel light, and interferes with a reference light provided by a plane wave so that interference fringes or fringe patterns are generated. The lens is adjusted on the basis of the interference fringes. In this method, an aberration of the group lens set is reflected in the interference fringes or fringe patterns. Accordingly, when the position of a second lens is moved with respect to a first lens such that the fringe patterns disappear and a monochromatic color is formed, the two lenses are accurately arranged positioned.
However, when this method is used, complicated processing is required to search a specific adjusting procedure from the interference fringes if no position of the group lens set is adjusted. Namely, an aberration must be normally analyzed by using a computer on the basis of the detected interference fringes. Therefore, it takes more than one minute to analyze the aberration since the fringe is scanned and a calculation is next made. Accordingly, no adjustment using the interference is conventionally practically used since it is inferior in working efficiency.
An object of the present invention is to provide an aberration measuring apparatus for accurately and easily detecting an aberration by utilizing interference fringe patterns.
Another object of the present invention is to provide an adjusting device for adjusting a position of a lens in a group lens set consisting of a plurality of lenses accurately and easily adjusted by utilizing the interference fringes.
In one aspect of the present invention, an aberration measuring apparatus for detecting aberration of a lens for converging an incident light beam passing therethrough is characterized by comprising a laser for emitting a light beam of a single wavelength; a dividing unit for dividing the light beam into first and second light beams; an optical system for guiding said first light beam to said lens; a reflector having a concave mirror surface consisting of a portion of a sphere, and reflecting said first light beam incident thereon after said first light beam passing through said lens is converged to a converging point; a detector for detecting an interference pattern created when said second light beam and said first light beam reflected by said reflector interfere with each other; a driving unit for moving said reflector with respect to an optical axis of said optical system; and an analyzer for analyzing the aberration of said lens. The driving unit displaces a center of said sphere from said converging point so as to change said interference pattern to an interference fringe pattern consisting of a plurality of circles approximately concentrically arranged. The analyzer determines the aberration of said lens on the basis of a distribution of said plurality of circles.
In another aspect of the present invention, an adjusting apparatus for detecting an aberration of a group lens set consisting of a plurality of lenses to adjust the aberration is characterized by comprising an aberration measuring apparatus having a laser for emitting a light beam of a single wavelength; a dividing unit for dividing the light beam into first light and second light beam; an optical system for guiding said first light beam to said lens group; a reflector having a concave mirror surface constituting one portion of a sphere and reflecting said first light beam incident thereon after said first light beam passing through said lens group is converged to a converging point; a detector for detecting an interference pattern in which said first light beam reflected by said reflector and said second light-interfere with each other; a driving unit for moving said reflector with respect to an optical axis of said optical system; and an analyzer for analyzing the aberration of said group lens set; and an adjusting mechanism for adjusting a position of one of said plurality of lenses with respect to a position of another lens and an inclination of the optical axis of one of said plurality of lenses in said group lens set. The driving unit displaces a center of said sphere from said converging point so as to change said interference pattern to an interference fringe pattern comprising a plurality of circles approximately concentrically arranged; and the adjusting mechanism adjusts the position of said one of said plurality of lenses with respect to the position of said another lens and the inclination of the optical axis of said one of said plurality of lenses in response to an output of said aberration measuring apparatus.